We present a microorganism-powered thermopneumatic pump that utilizes temperature-dependent slow-kinetics gas (carbon dioxide) generating fermentation of yeast as a pressure source. The pump consists of stacked layers of polydimethylsiloxane (PDMS) and a silicon substrate that form a drug reservoir, and a yeast-solution-filled working chamber. The pump operates by the displacement of a drug due to the generation of gas produced via yeast fermentation carried out at skin temperatures. The robustness of yeast allows for long shelf life under extreme environmental conditions (50 °C, >250 MPa, 5–8% humidity). The generation of carbon dioxide is a linear function of time for a given temperature, thus allowing for a controlled volume displacement. A polymeric prototype (dimensions 15 mm × 15 mm × 10 mm) with a slow flow rate of <0.23 μL min−1 and maximum backpressure of 5.86 kPa capable of continuously pumping for over two hours is presented and characterized. [Link to publication]

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A Skin-Contact-Actuated Dispense/Pump for Transdermal Drug Delivery

C. Mousoulis, M. Ochoa, B. Ziaie

Our group has developed a variety of micropump devices based on skin contact actuation for controllable transdermal drug delivery. Liquid to vapor phase-change of low boiling point fluorocarbon compounds is employed as the actuation mechanism, requiring no other external power source than the body heat. The induced actuation can result to a gradient of 1000 Pa/oC which is sufficient to drive liquid drug through microneedle arrays. Flowrate performance of 28.8 μL/min and 28.9 kPa backpressure has been illustrated. Single as well as multiple dosage is feasible with the use of unidirectional flap valves. The developed devices exhibit low fabrication costs, employment of biocompatible materials and battery-less operation, making them ideal single- or multiple-use transdermal drug dispensers. [C. Mousoulis et al., Proc. of MicroTAS, pp. 727-729, Groningen, Netherlands, October 2010. C. Mousoulis, et al., IEEE Trans. on Biomed. Eng., vol. 58, no. 5, pp. 1492-8, May. 2011.]

Laser-treated hydrophobic paper: an inexpensive microﬂuidic platform

G. Chitnis, Z. Ding, C.L. Chang, C.A. Savran, B. Ziaie

In this paper, we report a method for fabricating inexpensive microfluidic platforms on paper using laser treatment. Any paper with a hydrophobic surface coating (e.g., parchment paper, wax paper, palette paper) can be used for this purpose. We were able to selectively modify the surface structure and property (hydrophobic to hydrophilic) of several such papers using a CO2 laser. We created patterns down to a minimum feature size of 62 ± 1 µm. The modified surface exhibited a highly porous structure which helped to trap/localize chemical and biological aqueous reagents for analysis. The treated surfaces were stable over time and were used to self-assemble arrays of aqueous droplets. Furthermore, we selectively deposited silica microparticles on patterned areas to allow lateral diffusion from one end of a channel to the other. Finally, we demonstrated the applicability of this platform to perform chemical reactions using luminol-based hemoglobin detection. [Link to publication]

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Sequential droplet manipulation via vibrating ratcheted microchannels

Z. Ding, W.-B. Song, B. Ziaie

This work reports on a simple scheme for transport and sequential manipulation of droplets using ratchet-shaped microchannels. Once subjected to lateral vibration through a sinusoidal shaker with a controllable frequency and amplitude, droplets move along the direction of least resistance with velocities depending on vibration parameters (amplitude and frequency), channel geometry and material properties, and the angle between the channel and vibration direction (lateral offset angle). Using channels having different lateral offset angles, we achieved a controllable time delay between the transports of various droplets. Based on the same principal, we also designed a multi-functional droplet manipulation platform with the capability to transport, collect, mix, and discharge several droplets. [Link to publication]

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Aqueous microdrop manipulation and mixing using ferrofluid dynamics

W.-B. Song, Z. Ding, C. Son, and B. Ziaie

For droplet transport, a set of periodic lines of ferrofluid on top of a silicon wafer is created by a single strip magnet and dynamically changed by the rotation of a magnetic stirrer underneath it. It is demonstrated that the speed of droplet movement depends on the rotation speed of the magnetic stirrer as well as the size of the droplet. For better droplet mixing efficiency, a discontinuous pattern at the mixing spots is created by adding a smaller strip magnet to the above setup. [Link to publication]